How Medicare Part B Premiums Scale With Income

Medicare Part B covers outpatient medical services — physician visits, preventive care, durable medical equipment, and certain other services not handled under Part A's hospital benefit. Most enrollees pay a standard monthly premium, but a separate federal surcharge mechanism means a portion of beneficiaries pay considerably more based on their reported income.

That surcharge is called the Income-Related Monthly Adjustment Amount, or IRMAA. It is not a penalty and not a means-tested subsidy reduction; it is a legislatively defined premium tier system that layers additional charges on top of the standard Part B premium when a beneficiary's modified adjusted gross income crosses one of several fixed thresholds. The thresholds, the tier amounts, and the standard premium itself are recalculated each year.

How the IRMAA Tier Calculation Actually Works

The Social Security Administration, not Medicare directly, determines whether a beneficiary owes an IRMAA surcharge. SSA uses income data obtained from the Internal Revenue Service. The data used is not from the most recent tax year — it is from two years prior. A beneficiary enrolling in or paying Part B premiums in 2024 will have their IRMAA status determined using 2022 tax return data. This two-year lag is a structural feature of the system, not an error.

The income figure SSA examines is modified adjusted gross income (MAGI), which for this purpose is adjusted gross income as reported on the federal tax return plus any tax-exempt interest income. Capital gains, required minimum distributions from traditional IRAs and 401(k) plans, and other taxable income all flow into this figure. The MAGI of both spouses is combined for married couples filing jointly, and separate thresholds apply to married individuals who file separately from their spouse.

Once SSA has the MAGI figure, it compares it against a set of income brackets. For 2024, the standard Part B premium is $174.70 per month. Beneficiaries whose 2022 MAGI falls at or below $103,000 (individual filers) or $206,000 (joint filers) pay only the standard premium. Above those thresholds, five additional IRMAA tiers apply, with total monthly premiums — standard premium plus surcharge — rising through each bracket. At the highest tier, for individual filers with 2022 MAGI above $500,000 (or joint filers above $750,000), the 2024 total monthly Part B premium reaches $594.00. These figures are published annually by the Centers for Medicare and Medicaid Services and are subject to change each calendar year.

IRMAA surcharges for Part B are collected by deducting the total premium directly from the beneficiary's monthly Social Security benefit payment. Beneficiaries who are not yet receiving Social Security benefits — or whose Social Security payment is insufficient to cover the premium — receive a bill from Medicare and pay separately.

Which Agencies Administer the Income-Based Premium System

Three federal entities are involved in the Part B IRMAA process, each with a distinct function. The Internal Revenue Service holds the tax return data that contains the MAGI figure. IRS does not set premiums or make coverage decisions; it supplies the income data to SSA under an established data-sharing arrangement.

The Social Security Administration receives that income data, applies the IRMAA tier thresholds, and issues the initial determination notice to the beneficiary. SSA also processes appeals — called reconsiderations — when a beneficiary disputes the income figure used or believes the correct tier has not been applied. SSA is the administrative contact point for IRMAA disputes, not Medicare or CMS directly.

The Centers for Medicare and Medicaid Services sets the standard Part B premium and the IRMAA tier amounts each year. CMS publishes those figures in the annual Medicare & You handbook and in formal rulemaking. CMS also administers the underlying Part B benefit — the coverage rules, cost-sharing structure, and provider payment rates — but the income-based premium determination flows through SSA.

Where the Income-Based Premium Calculation Produces Unexpected Results

The two-year income lag is the most common source of unexpected IRMAA charges. A beneficiary who retired in 2023 and whose income dropped substantially may still owe a surcharge in 2024 based on their higher 2022 working income. The system does not automatically detect the income change; the prior return's data governs unless the beneficiary actively files an appeal with SSA using a Life-Changing Event form (SSA-44).

A one-dollar income increase that crosses a tier threshold produces a full tier jump, not a proportional increase. Because the tiers are cliffs rather than a continuous scale, a beneficiary with MAGI just above a threshold pays the same surcharge as a beneficiary with income substantially higher — until the next threshold is reached. This cliff structure means that certain income events, such as a large Roth conversion, a property sale, or a year with unusually high required minimum distributions, can trigger a tier increase for the following premium year even when the income event was non-recurring.

Married couples filing separately face a distinct and often surprising schedule. The income thresholds for married-filing-separately are not half of the joint thresholds; they are set much lower, meaning a beneficiary who files separately from a high-income spouse can reach upper IRMAA tiers at a lower individual income than a beneficiary filing jointly.

Finally, the IRMAA determination applies independently to Part D prescription drug coverage as well. A beneficiary enrolled in both Part B and a Part D plan will receive separate IRMAA surcharges for each, and the combined effect on total monthly premium costs can be substantially larger than the Part B surcharge alone.

What the IRMAA Notice and Medicare Account Record Show

When SSA determines that a beneficiary owes an IRMAA surcharge, it issues a written notice — typically titled "Initial IRMAA Determination" — that states the income tier applied, the tax year of the data used, the resulting monthly premium amount, and the deadline and process for requesting a reconsideration. The notice does not show the underlying tax return figures; it shows only which bracket was triggered and the resulting premium.

The Medicare Summary Notice, which is a periodic statement of Part B claims activity, shows the standard premium amount applied to claims but does not itemize the IRMAA surcharge separately. The surcharge appears instead on the Social Security benefit statement as a deduction from the monthly payment, listed alongside the base Part B premium. Beneficiaries who pay by direct billing rather than Social Security deduction see the total combined premium on their Medicare bill, but the bill itself may not break out the standard premium and surcharge as separate line items in all presentation formats.

The SSA online account portal, my Social Security, shows the current Part B premium amount being deducted but does not display the income tier rationale or the IRS data year used. A beneficiary seeking to verify which tax year drove the determination must reference the original IRMAA notice or contact SSA directly.

The Part B premium system is one of the few places in Medicare where income explicitly determines cost, and the structural reliance on two-year-old IRS data means the premium amount in any given year reflects financial circumstances that may no longer apply to the beneficiary paying it.

Note: This explains how a retirement system works. It is not financial, tax, or legal advice, it is not specific to any individual's retirement, and it is not a substitute for a licensed financial, tax, or legal professional. Rules, ages, and dollar limits change by year — check the cited sources.